Although the Pathetique Sonata is indeed one of the most often played, the fact remains that it is nonethless on the list. I can't think that the examiners would hold that against you. They will surely have heard every Beethoven sonata a zillion times before anyway.
Agreed, I wouldn't discourage the Pathetique if showpan were confident in her ability to play it well, but since she had reservations about it anyway, it seems safer to choose something else.
showpan: If you're dropping the Pathetique for the Ravel (which I would be inclined to advise), maybe try a set of variations? Haydn's Variations in F minor or Mozart's Duport Variations should fit well... the other sets (Mozart K. 455, Beethoven F major and C minor) might be a bit too long, but I'm not sure.
Regarding general questions, I think the biggest thing I would have changed was preparing better for the Viva. The examiners LOVED my programme notes, but were less enthusiastic about my actual spoken performance... so make sure you're familiar with lots of things they "might" possibly ask. I ended up with 15/25, which was well above passing, but I was somewhat disappointed since I always thought it would be my best section. Regarding the quick study, just remember that actual notes are less important than observing dynamics, style, etc. - a wooden, note-perfect performance will score lower than a performance with a few flubs that captures the "essence". Also, make sure you isolate the difficult parts first rather than just reading through, because full read-throughs can take up substantial portions of the 5 min. preparation.
I actually took the exam twice - I failed the recital section by two points the first time (in all fairness, it was just 6 months after grade

, passed the other sections but decided to retake the Viva in addition to the recital since I thought I could improve it. So when I retook the exam 6 months ago, I was only doing the recital and viva. When I took the exam the first time, I did the recital first, then quick study, and ended with viva. I chose to do the recital first since I was most nervous about it (as kevinr said), and thought it would impair my performance on the quick study and viva (which require more "on the spot" skills) if I was worrying about it.
I hope this helps! If you want more support, the ABRSM website has a fairly active forum in which more people will know about the diplomas (this particular forum is US-based, so fewer people have experience with them).
Kelly